Super no-scale models in string theory

Understand

We consider "super no-scale models" in the framework of the heterotic string, where the N=4,2,1 --> 0 spontaneous breaking of supersymmetry is induced by geometrical fluxes realizing a stringy Scherk-Schwarz perturbative mechanism.

• Classically, these backgrounds are characterized by a boson/fermion degeneracy at the massless level, even if supersymmetry is broken.
• At the 1-loop level, the vacuum energy is exponentially suppressed, provided the supersymmetry breaking scale is small, m_{3/2} << M_{string}.
• We show that the &#34;super no-scale string models&#34; under consideration are free of Hagedorn-like tachyonic singularities, even when the supersymmetry breaking scale is large, m_{3/2} ~ M_{string}.